AVI systems are used in the clinical packaging environment for quality control purposes. In particular, AVI systems may be used to test syringes, such as those used in auto-injector pens, for example, for the proper plunger (i.e., rubber piston or stopper) depth. For auto-injector syringes, the position of the plunger within the syringe is of particular importance, as a plunger depth falling outside of a specified range of depth measurements may cause the auto-injector to malfunction or provide an incorrect dosage. For example, if the plunger is positioned too low in the syringe (i.e., towards the needle) the spring-activated piston used by the auto-injector pen may travel a longer distance before contact, thereby gathering excessive kinetic energy. This may produce a shockwave down the glass body of the syringe upon contact with the plunger, resulting in glass-breakage near the tapered needle-end. Moreover, plunger depth measurement is an important check in controlling the filling process and ensuring container closure integrity.
Traditional AVI systems measure plunger depth by identifying a top edge of the syringe flange and a top edge of the plunger, determining the difference between these two edges in terms of pixels, and then converting the pixel value to a linear real-world measurement based upon a conversion factor. However, due to the manufacturing process, glass syringe flanges typically have a somewhat uneven and unpredictable shape, and may include undulations that make it difficult for typical image processing algorithms to accurately identify the flange top edge. Furthermore, because the testing procedure is often conducted in an area that is not a cleanroom environment, dust or debris may settle on the syringe flange, causing traditional image processing techniques to incorrectly identify the top edge of the flange as an area associated with such artifacts. Further compounding this problem, defects in the trays holding the syringes may carry over into the image being analyzed, and typical image processing techniques may incorrectly identify such defects in the tray as the top edge of the flange.
Regarding the measurement of the top edge of the plunger, conventional image analyses such as edge detection function to identify the top and side edges of the plunger within a fixed region of interest (ROI). Using this information, conventional AVI systems typically identify the plunger centerline and use the intersection of the centerline with the top edge of the plunger as a reference by which to measure the plunger depth from the top edge of the flange. However, these techniques are constrained by the use of a fixed ROI, and therefore such conventional systems may only be used to test a single size and type of syringe. Furthermore, tray features used to secure each syringe within the tray may partially obscure the plunger and/or the operator may fail to align the syringes properly, causing edge detection techniques to fail. Further complicating this issue, blemishes on the syringe container wall and/or plunger dimples that exist along the top edge of the plunger may cause typical edge-detection algorithms to fail or to incorrectly identify the uppermost edge of the plunger. As a result, typical AVI systems used for syringe testing have several drawbacks.